**10. Redox relay as a hypothetical carrier for redox signaling**

It has been established that the content of glutathione (GSH) is rather low in pancreatic β-cells [177–180], in contrast to the content of thioredoxins and

glutaredoxins [181, 182], peroxiredoxins and other proteins capable of redox relay. Therefore, these proteins are able to conduct and spread the redox signals [183, 184]. From this point of view, the pancreatic β-cell appears to be a wellintegrated redox system.

Redox signal spreading may be accomplished either by the direct diffusion of H2O2 or may be facilitated by the specialized proteins. Redox signals can be traced experimentally as instantly oxidatively modified cysteine residues, which are spread via different sets of proteins in different tissues. However, one may consider their majority as passive targets. For the case of NOX4 residing in the proximity of KATP, undoubtedly, the direct diffusion of H2O2 would be sufficient. Nevertheless for more distant NOX4 molecules, this would be difficult. Also, for mitochondrial redox signaling towards targets residing in the plasma membrane, a distance over 500 nm must be overcome. Redox signal across such high distances could be conducted through the action of thiol-based proteins capable of redox relay to the target, such as peroxiredoxins (regenerated via thioredoxins and glutaredoxins). The relay would provide a common redox signal transfer. It is yet to be established whether a redox relay exists via an array of peroxiredoxin oligomers.
